Potential asteroid impact on April 1 2009

Bruce Perens

Wed Oct 01 05:11:36 -0700 2008

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And the message there is interesting:

Virtual Impactors

We would like to thank the people who have observed the two asteroids we were
interested in, namely 2008SH82 and 2008SV11.

Unfortunately, for SV11 the alarm is not over, the date of possible impact
has shifted to April 1, 2009, but it is NOT an April's fool.

We need this object to be observed soon, but without overdoing. The prediction
uncertainty grows quickly in the next few days while the apparent magnitude is
stationary, thus we need a set of observatiosn as much as possible uniformly
spread in time. Please DO NOT send to MPC tens, or even hundreds, of
observations in the same night, as it happened with 2004MN4 (later named
Apophis) in the last days of 2004. Because of systematic errors, mostly due to
catalog errors, which cannot be properly compensated because of the lack of
suitable information transmitted to us (e.g., signal to noise and catalog used
for reduction) such an excess of data results in a worse orbit; we end up by
deleting most of such overdense data from the solution. The observers are asked
to provide few data of the best possible astrometric quality. If you are forced
to use image stacking, please send a single data point for the entire stack.

With your help, this problem is likely to be solved in few days, at most few
weeks.

Yours

Andrea Milani

================================================
Andrea Milani Comparetti
Dipartimento di Matematica
Piazzale B. Pontecorvo 5
56127 PISA ITALY

tel. +39-050-2213254 fax +39-050-2213224
cellular phone +39-349-4482751
E-mail: milani@...
WWW: http://adams.dm.unipi.it/~milani/
================================================

Potential asteroid impact on April 1 2009

phred14

Wed Oct 01 06:58:35 -0700 2008

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I'm not quite sure how to read the tables.  I don't see mass or direct size anywhere.  How big is this thing, how many equivalent megatons?

Looking at the "Close Approaches" table and seeing the "Palmero -2" it sounds as if there's roughly a 1% chance of impact, though obviously they're asking for better data to refine that.  From the "minimum possible distance" column in the table, there are 3 entries with "0", (impact?) in 1992, 2026, and 2060.  Next year's minimum is currently listed at about 3 times the distance to the Moon, but with a probability of "1", where the entries with "0" have much lower probabilities.

So my impression is that the other 3 approaches might hit the Earth, but have a relatively low chance of doing so.  This approach is highly likely to be close, but is not likely to hit.  Again, they're asking for more data to refine their estimates.  Is this a correct impression?

Potential asteroid impact on April 1 2009

peacefinder

Wed Oct 01 10:29:34 -0700 2008

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The tracker appears to have been updated with new information, dropping the object's cumulative Palermo rating to -3.02 as of this writing. The data you're looking for about this object's size, mass, and impact energy can be found off of this table. More generally, you can look at the table of all objects (well, all known objects) with some hypothetical risk and click the object designator link for the details of all potential impacts.

Typically these things pop up on the scale at a rather high risk level right after discovery, because so little is known about their orbits. Within a week, usually, enough observations come in to define the elements precisely enough to make a better evaluation of the impact risk. I find that it's generally best to ignore any object that has an observation span of under a week, and it's not worth getting exited unless the risk holds at a high level for two weeks. (Although I'm glad NEO astronomers are excited, as a layman I don't need to be.)

This object has been observed over a span of just over five days (as of this writing) so its precise orbit is just now coming in to focus. Already it has fallen below quite a few older objects in terms of overall risk.

Potential asteroid impact on April 1 2009

Michael Smith

Thu Oct 02 03:44:08 -0700 2008

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Typically these things pop up on the scale at a rather high risk level right after discovery, because so little is known about their orbits. Within a week, usually, enough observations come in to define the elements precisely enough to make a better evaluation of the impact risk.

It seems strange to me that the Palermo rating doesn't take into account this type of uncertanty.

Potential asteroid impact on April 1 2009

peacefinder

Thu Oct 02 15:18:32 -0700 2008

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It does take that into account. Consider what happens, though: A newly-discovered object's orbit gets defined based on some minimal data. The data contains uncertainties, so our knowledge of its path looks less like a single path than like a broad probablility cloud; its true path could lie anywhere within the cloud. As new observational data data comes in and the orbit model is refined, the cloud gets smaller. While the probability cloud shrinks, and until the cloud no longer intersects the Earth, the apparent probability of impact will climb.

Most likely, the probability cloud will shrink with more data until it no longer intersects Earth at all, in which case the collision is ruled out and the object can be ignored. Less likely, the probability cloud will shrink with more data until the Earth just brushes through the edge of it, and the likelihood of impact falls to something requiring scientific notation with a large negative exponent. (Still the object is a risk, and more observations should be made, but not urgently.) In either case what we laymen see is an increasing probability of impact, followed by a precipitous (meteoric?) drop.

Very rarely, of course, we could see an object's probability of impact keep climing to 1.0. Hasn't happened yet.

Ultimately the problem is not with the scale. Instead, the problem is that people tend to report on it before allowing a reasonable time to pass; then the folks who read those reports without knowing the context tend to get all excited before that's really warranted by the data. The scale is really useful to lots of people - especially NEO astronomers wondering what they ought to be observing tonight - but it's not so great for the front page of USA Today.

Potential asteroid impact on April 1 2009

peacefinder

Mon Oct 06 18:45:09 -0700 2008

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Of course, it's always possible that I spoke too soon. :-)

good post!

zogger

Wed Oct 01 08:13:34 -0700 2008

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Hey, cool, keep us updated! I need to know if I need to plan my end 0 de world free BBQ or not.

good post!

ah.clem

Wed Oct 01 13:04:20 -0700 2008

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Zog, have it anyway!  I was thinking of having an "End o' the Economic World" party, myself.

ah.clem

I like that

zogger

Wed Oct 01 20:10:20 -0700 2008

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Looks to be the bovine exhaust might be impacting the impeller next week maybe, so a nice "heck with it!" BBQ sounds good.